Message-ID: <52012B35.90801@intel.com>
Date: Tue, 06 Aug 2013 09:58:29 -0700
From: Dave Hansen <dave.hansen@intel.com>
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To: Krzysztof Kozlowski <k.kozlowski@samsung.com>
CC: Seth Jennings <sjenning@linux.vnet.ibm.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Kyungmin Park <kyungmin.park@samsung.com>
Subject: Re: [RFC PATCH 3/4] mm: add zbud flag to page flags
References: <1375771361-8388-1-git-send-email-k.kozlowski@samsung.com> <1375771361-8388-4-git-send-email-k.kozlowski@samsung.com>
In-Reply-To: <1375771361-8388-4-git-send-email-k.kozlowski@samsung.com>
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On 08/05/2013 11:42 PM, Krzysztof Kozlowski wrote:
> +#ifdef CONFIG_ZBUD
> +	/* Allocated by zbud. Flag is necessary to find zbud pages to unuse
> +	 * during migration/compaction.
> +	 */
> +	PG_zbud,
> +#endif

Do you _really_ need an absolutely new, unshared page flag?
The zbud code doesn't really look like it uses any of the space in
'struct page'.

I think you could pretty easily alias PG_zbud=PG_slab, then use the
page->{private,slab_cache} (or some other unused field) in 'struct page'
to store a cookie to differentiate slab and zbud pages.
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